Magnetic single-wall memories such as magnetic bubble memories are well known in the art. A familiar form of such memories employs a layer of material in which bubbles can be moved and a pattern of magnetic elements, typically of permalloy, which defines propagation channels in the layer. The propagation elements respond to a magnetic field reorienting in the plane of the layer to move bubbles along the channels to a detector arrangement typically also made of permalloy. A bubble memory of this form is commonly referred to as a "field access" bubble memory.
The detector arrangement comprises a succession of stages of a channel where each stage has a number of elements closely spaced apart and aligned transverse to the direction of bubble movement. The numbers of elements in sucessive ones of the stages increase in the direction of bubble movement to a maximum at a detector stage. The elements in the detector stage are linked together to form a single magnetoresistive element astride the bubble path for detecting a bubble which is laterally elongated due to the increasing numbers of elements in the stages preceding and including the detector stage. The elements of the detector arrangement are normally of V-shaped geometry, the plurality of elements in each stage generating a moving wave of attractive poles for elongating as well as for moving a bubble.
The forward motion of a bubble in the detector arrangement is known to be non-uniform. That is to say, movement of an elongated bubble during one phase of a rotating field cycle is faster than in another phase. Consequently, as frequency of operation increases for a material of a given mobility, a maximum speed is reached more quickly than would be reached if a more uniform speed could be achieved.
In addition, the interlinked elements of the detector stage introduce patterns of strong and weak poles for some orientations of the rotating drive fields. These poles, on occasion, cause the elongated bubbles to assume irregular shapes thus leading to reduced margin ranges. For presently available materials, device failures due to problems of this sort manifest themselves at frequencies approaching four hundred kilohertz and at temperatures of about 0.degree. and below.